Role of plume convection and remelting on the mushy layer structure during directional solidification

Abstract

In the present work, solidification of a hyper-eutectic ammonium chloride solution in a bottom-cooled rectangular cavity (i.e. with stable thermal gradient) is numerically simulated. The role of finger convection and remelting on the structure of a mushy layer containing channels is studied. The numerical simulation is performed using a fixed-grid single-domain approach in which local remelting and anisotropic variation of mush permeability are taken into account. It is observed that solute-rich liquid rising in the form of finger convection causes delayed growth and localized remelting of portions of the solid/mush interface, resulting in patches of thin structure known as channels. The present study reveals the manner in which the structure of a mushy layer evolves during channel formation. Effects of bulk liquid convection on channel formation, evolution, destruction and the resulting effect on the mush structure are found to be significant. Numerical prediction with regard to variation of the number of channels with time agrees qualitatively with published experimental results.